The present invention relates generally to interface devices between humans and computers, and more particularly to computer input devices that provide force feedback to the user.
Computer systems can be used for a variety of applications, including simulations and games which are very popular with consumers. A computer system typically displays a visual environment to a user on a display screen or other visual output device. Users can interact with the displayed environment to perform functions on the computer, such as playing a game, experience a simulation or virtual reality environment, use a computer aided design system, operate a graphical user interface (GUI), perform file manipulation, or otherwise influence events or images depicted on the screen. Such user interaction can be implemented through the use of a human-computer interface device, such as a joystick, mouse, trackball, stylus, tablet, or the like, that is connected to the computer system controlling the displayed environment. Typically, the computer updates the environment in response to the user's manipulation of a user-manipulatable physical object such as a joystick handle or mouse, and provides visual feedback to the user utilizing the display screen and, typically, audio speakers. The computer senses the user's manipulation of the object through sensors provided on the interface device.
One common use for computer and virtual reality systems is for simulations and games. For example, a user can operate a simulated fighter aircraft or spacecraft by manipulating controls such as a joystick and other buttons and view the results of controlling the aircraft on display device portraying a virtual reality simulation or game of the aircraft in flight. In other applications, a user can manipulate objects and tools in the real world, such as a stylus, and view the results of the manipulation in a virtual reality world with a "virtual stylus" viewed on a screen, in 3-D goggles, etc. In yet other applications, activities such as medical procedures, vehicle training, etc., virtual reality computer systems and simulations are used for training purposes to allow a user to learn from and experience a realistic "virtual" environment.
In addition to sensing and tracking a user's manual activity and feeding such information to the controlling computer to provide a 3D visual representation to the user, a human interface mechanism should also provide tactile or haptic feedback to the user, more generally known as "force feedback." The need for the user to obtain realistic force information and experience force sensation is extensive in many kinds of simulation and greatly enhances an experience of a virtual environment or game. For example, in a simulated environment, the impact of a user controlled object against a "virtual wall" should feel as if a hard object were impacted. Similarly, in 3-D virtual world simulations where the user can manipulate objects, force feedback is necessary to realistically simulate physical objects; for example, if a user touches a pen to a table, the user should feel the impact of the pen on the table. For simulations or games involving controlled vehicles, force feedback for controls such as a joystick can be desirable to realistically simulate experienced conditions, such as high acceleration in an aircraft, or the viscous, mushy feel of steering a car in mud. An effective human interface not only acts as an input device for tracking motion, but also as an output device for producing realistic force or "feel" sensations.
Force feedback interface devices can provide physical sensations to the user manipulating a user manipulable object of the interface device through the use of computer-controlled actuators, such as motors, provided in the interface device. In most of the prior art force feedback interface devices, the host computer directly controls forces output by controlled actuators of the interface device, i.e., a host computer closes a control loop around the system to generate sensations and maintain stability through direct host control. This configuration has disadvantages in the inexpensive mass market, since the functions of reading sensor data and outputting force values to actuators can be a burden on the host computer's processor which detracts from the performance of the host in other host tasks and application execution. In addition, low bandwidth interfaces are often used, which reduces the ability of the host computer to control realistic forces requiring high frequency signals.
For example, in one type of force feedback interface described in U.S. Pat. No. 5,184,319, by J. Kramer, force and texture information is provided to a user. The interface consists of an glove or "exoskeleton" which is worn over the user's appendages, such as fingers, arms, or body. Forces can be applied to the user's appendages using tendon assemblies and actuators controlled by a computer system to simulate force and textual feedback. However, the system described by Kramer includes a host computer directly controlling the actuators of the device, and thus has the disadvantages mentioned above. In addition, the Kramer device is not easily applicable to simulated environments where an object is referenced in virtual space and force feedback is applied to the object. The forces applied to the user in Kramer are with reference to the body of the user; the absolute location of the user's appendages are not easily calculated. In addition, the exoskeleton devices of Kramer can be complex, cumbersome or even dangerous to the user if extensive devices are worn over the user's appendages.
Typical multi-degree-of-freedom apparatuses that include force feedback also include several other disadvantages. Since actuators which supply force feedback tend to be heavier and larger than sensors, they would provide inertial constraints if added to a device. There is also the problem of coupled actuators, where each actuator is coupled to a previous actuator in a chain such that a user who manipulates the object must carry the inertia of all of the subsequent actuators and links except for the first actuator in the chain. These types of interfaces also introduce tactile "noise" to the user through friction and compliance in signal transmission and limit the degree of sensitivity conveyed to the user through the actuators of the device.
In other situations, low-cost and portable mechanical interfaces having force feedback are desirable. Active actuators, such as motors, generate forces on an interface device and the user manipulating the interface device so that the interface device can move independently of the user. While active actuators often provide quite realistic force feedback, they can also be quite bulky and typically require large power supplies to operate. In addition, active actuators typically require high speed control signals to operate effectively and provide stability. In many situations, such high speed control signals and high power drive signals are not available or too costly, especially in the competitive, low-cost market of personal computers. Furthermore, active actuators can sometimes prove unsafe for a user when strong, unexpected forces are generated on a user of the interface who does not expect those forces.